Piezoelectric biosensor and related method of formation

ABSTRACT

In some embodiments, a piezoelectric biosensor is provided. The piezoelectric biosensor includes a semiconductor substrate. A first electrode is disposed over the semiconductor substrate. A piezoelectric structure is disposed on the first electrode. A second electrode is disposed on the piezoelectric structure. A sensing reservoir is disposed over the piezoelectric structure and exposed to an ambient environment, where the sensing reservoir is configured to collect a fluid comprising a number of bio-entities.

REFERENCE TO RELATED APPLICATION

This Application claims the benefit of U.S. Provisional Application No.62/738,665, filed on Sep. 28, 2018, the contents of which are herebyincorporated by reference in their entirety.

BACKGROUND

Biosensors are devices for sensing and detecting bio-entities, andtypically operate on the basis of electronic, chemical, optical, ormechanical detection principles. Detection can be performed by detectingthe bio-entities themselves, or through interaction and reaction betweenspecified reactants and the bio-entities. Biosensors are widely used indifferent life-science applications, ranging from environmentalmonitoring and basic life science research to Point-of-Care (PoC)in-vitro molecular diagnostics.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of apiezoelectric biosensor.

FIG. 2 illustrates some other embodiments of the piezoelectric biosensorof FIG. 1 .

FIG. 3 illustrates some other embodiments of the piezoelectric biosensorof FIG. 1 .

FIGS. 4-14 illustrate a series of cross-sectional views of someembodiments of a method for forming the piezoelectric biosensor of FIG.3 .

FIG. 15 illustrates a flowchart of some embodiments of a method forforming a piezoelectric biosensor.

DETAILED DESCRIPTION

The present disclosure will now be described with reference to thedrawings wherein like reference numerals are used to refer to likeelements throughout, and wherein the illustrated structures are notnecessarily drawn to scale. It will be appreciated that this detaileddescription and the corresponding figures do not limit the scope of thepresent disclosure in any way, and that the detailed description andfigures merely provide a few examples to illustrate some ways in whichthe inventive concepts can manifest themselves.

The present disclosure provides many different embodiments, or examples,for implementing different features of this disclosure. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Some biosensors analyze a sample by passing radiation through the sampleand measuring an amount of radiation absorbed by the sample. One exampleof such a biosensor is a spectrophotometer. Some spectrophotometersanalyze a sample by comparing light transmittance of a blank samplecomprising a bio-entity (e.g., a sample that does not contain a coloringagent) to light transmittance of a colored sample comprising abio-entity (e.g., a sample containing a coloring agent). By comparingthe light transmittance of the blank sample to the light transmittanceof the colored sample, certain properties of the colored/blank samplemay be determined.

One challenge with the above biosensors is manufacturing/operatingcosts. The above biosensors require components (e.g., light emittingdevices, beam splitters, light detectors, etc.) that are expensive tomanufacture. Further, analyzing a sample with the above biosensors istime intensive due to the need to run multiple samples (e.g., blank andcolored) through time intensive bio-testing procedures, therebyincreasing the cost to analyze the sample. In addition, the abovebiosensors are typically enclosed in a large housing that hinders theuse of the above biosensors in Point-of-Care (PoC) applications, therebyfurther increasing the cost to analyze the sample.

In various embodiments, the present application is directed toward apiezoelectric biosensor. The piezoelectric biosensor comprises apiezoelectric structure disposed between a first electrode and a secondelectrode, where the first electrode is disposed over a semiconductorsubstrate. A sensing reservoir configured to collect a fluid comprisinga number of bio-entities is disposed over the piezoelectric structure.The piezoelectric biosensor is configured to analyze a specific propertyof the bio-entities (e.g., detecting bio-entity growth in the fluid,detecting neurotransmission activity between bio-entities in the fluid,etc.) in the sensing reservoir. In some embodiments, an electricalproperty (e.g., capacitance, voltage, etc.) of the piezoelectricbiosensor varies as the number of bio-entities in the sensing reservoirvaries. Thus, the piezoelectric biosensor may analyze the specificproperty of the bio-entities.

Because the piezoelectric biosensor is disposed on a semiconductorsubstrate, the cost to manufacture the piezoelectric biosensor may beless expensive than other types of biosensors (e.g., spectrophotometers,plate readers, etc.). In addition, because the piezoelectric biosensoris disposed on a semiconductor substrate, a form factor of thepiezoelectric biosensor may be smaller than other types of biosensors.Thus, the piezoelectric biosensor may reduce the cost to analyze asample by providing an inexpensive PoC biosensor application. Further,testing a sample (e.g., a fluid comprising a number of bio-entities)with the piezoelectric biosensor may be less time intensive than othertypes of biosensors due to the piezoelectric biosensor having asimplified bio-testing procedure (e.g., testing one sample to determinethe specific property of the bio-entities). Thus, the piezoelectricbiosensor may further reduce the cost to analyze a sample.

FIG. 1 illustrates a cross-sectional view of some embodiments of apiezoelectric biosensor 100.

As shown in FIG. 1 , the piezoelectric biosensor 100 comprises asemiconductor substrate 102. The semiconductor substrate 102 has afront-side 102 f, and a back-side 102 b that is opposite the front-side102 f. In some embodiments, the semiconductor substrate 102 comprisesany type of semiconductor body (e.g., monocrystalline silicon/CMOS bulk,silicon-germanium (SiGe), silicon on insulator (SOI), etc.). In furtherembodiments, the semiconductor substrate 102 may have a thickness (e.g.,a distance between the front-side 102 f and the back-side 102 b) ofabout 750 micrometers (μm).

A first electrode 104 is disposed over the semiconductor substrate 102.In some embodiments, the first electrode 104 is disposed over thefront-side 102 f of the semiconductor substrate 102. In furtherembodiments, the first electrode 104 may comprise, for example, titanium(Ti), platinum (Pt), copper (Cu), gold (Au), aluminum (Al), zinc (Zn),tin (Sn), ruthenium (Ru), some other conductive material, or acombination of the foregoing. In other embodiments, the first electrode104 may comprise, for example, titanium dioxide (TiO₂), a rutheniumoxide (RuO_(X)), indium tin oxide (ITO), some other metal based oxide,or a combination of the foregoing.

A piezoelectric structure 106 is disposed on the first electrode 104. Insome embodiments, the piezoelectric structure 106 may comprise, forexample, zinc oxide (ZnO), gallium nitride (GaN), lead zirconatetitanate (PZT), some other piezoelectric material, or a combination ofthe foregoing.

A second electrode 108 is disposed on the piezoelectric structure 106.In some embodiments, the second electrode 108 comprises, for example,Ti, Pt, Cu, Au, Al, Zn, Sn, Ru, some other conductive material, or acombination of the foregoing. In other embodiments, the second electrode108 may comprise, for example, TiO₂, RuO_(X), ITO, some other metalbased oxide, or a combination of the foregoing. In further embodiments,the second electrode 108 and the first electrode 104 comprise a sameconductive material.

In some embodiments, a passivation layer 110 is disposed over the secondelectrode 108. In further embodiments, the passivation layer 110 extendsthrough the second electrode 108 and the piezoelectric structure 106 tothe first electrode 104. In further embodiments, the passivation layer110 may comprise, for example, an oxide (e.g., silicon dioxide (SiO₂)),a nitride (e.g., silicon nitride (SiN)), an oxy-nitride (e.g., siliconoxy-nitride (SiO_(X)N_(Y))), or the like. In yet further embodiments,the passivation layer 110 may comprise a metal based oxide (e.g.,aluminum oxide (Al₂O₃)).

A first input/output (I/O) structure 112 (e.g., a pad, solder ball,etc.) is electrically coupled to the first electrode 104. In someembodiments, the first I/O structure 112 is disposed over the firstelectrode 104 and extends through the second electrode 108 and thepiezoelectric structure 106 to contact the first electrode 104. Infurther embodiments, the passivation layer 110 separates the first I/Ostructure 112 from the piezoelectric structure 106 and the secondelectrode 108.

A second I/O structure 114 (e.g., a pad, solder ball, etc.) iselectrically coupled to the second electrode 108. In some embodiments,the second I/O structure 114 is disposed over the second electrode 108and extends through the passivation layer 110 to contact the secondelectrode 108. In further embodiments, the first I/O structure 112 andthe second I/O structure 114 may comprise, for example, Ti, Au, Cu, Al,some other conductive material, or a combination of the foregoing. Infurther embodiments, the first I/O structure 112 and the second I/Ostructure 114 are configured to provide electrical connections from thefirst electrode 104 and the second electrode 108, respectively, toprocessing circuitry (not shown) (e.g., an external microprocessor,measurement circuitry, bias circuitry, etc.). In yet furtherembodiments, the processing circuitry may be disposed on a semiconductorsubstrate (not shown) that is discrete from the semiconductor substrate102 in which the piezoelectric structure 106 is disposed over. In otherembodiments, the processing circuitry may be disposed on a samesemiconductor substrate 102 as the piezoelectric structure 106.

A sensing reservoir 116 is disposed over the piezoelectric structure106. The sensing reservoir 116 is configured to collect a fluid 118comprising a number of bio-entities 120 (e.g., cells, neurons, etc.). Insome embodiments, a fluidic channel 122 is disposed on the passivationlayer 110. The fluidic channel 122 is a structure that is configured toimprove/direct a flow of the fluid 118 into the sensing reservoir 116.In further embodiments, the fluidic channel 122 may be spaced from boththe first I/O structure 112 and the second I/O structure 114. In yetfurther embodiments, the fluidic channel 122 may comprise, for example,polysilicon, an oxide (e.g., SiO₂), a nitride (e.g., SiN), anoxy-nitride (e.g., SiO_(X)N_(Y)), or the like.

In some embodiments, the sensing reservoir 116 is defined by a topsurface of the piezoelectric structure 106, opposite sidewalls of thesecond electrode 108, opposite sidewalls of the passivation layer 110,and opposite sidewalls of the fluidic channel 122. For example, a bottomof the sensing reservoir 116 is defined by the top surface of thepiezoelectric structure 106, and sides of the sensing reservoir 116 aredefined by the opposite sidewalls of the second electrode 108, theopposite sidewalls of the passivation layer 110, and the oppositesidewalls of the fluidic channel 122, respectively. In furtherembodiments, the opposite sidewalls of the second electrode 108, theopposite sidewalls of the passivation layer 110, and the oppositesidewalls of the fluidic channel 122 may be substantially aligned,respectively. In yet further embodiments, the sides of the sensingreservoir may be substantially vertical.

The piezoelectric biosensor 100 is configured to analyze a specificproperty of the bio-entities 120 (e.g., detecting bio-entity growth inthe fluid, detecting neurotransmission activity between bio-entities inthe fluid, etc.) in the sensing reservoir 116. For example, thepiezoelectric biosensor 100 is configured to detect a number ofbio-entities 120 in the sensing reservoir 116. In some embodiments, as anumber of bio-entities 120 in the sensing reservoir 116 changes, amechanical stress applied to the piezoelectric structure 106 willchange, resulting in a change in an electric potential across thepiezoelectric structure 106. The change in electric potential allows thepiezoelectric biosensor 100 to detect the number of bio-entities 120 inthe sensing reservoir 116 due to an electrical property (e.g.,capacitance, voltage, etc.) of the piezoelectric biosensor 100 varyingas the number of bio-entities 120 in the sensing reservoir 116 varies.

For example, in some embodiments, the piezoelectric structure 106 isconfigured to change its shape based on the number of bio-entities 120in the sensing reservoir 116. For example, the piezoelectric structure106 may have a first shape when zero bio-entities 120 are in the sensingreservoir 116, a second shape different than the first shape when onebio-entity 120 is disposed in the sensing reservoir, and a third shapedifferent than the first and second shape when a plurality ofbio-entities 120 are disposed in the sensing reservoir 116. In someembodiments, the piezoelectric structure 106 may change its shape basedon the number of bio-entities 120 in the sensing reservoir 116 due to amechanical stress exerted on the piezoelectric structure 106 varying asthe number of bio-entities 120 in the fluid 118 varies. In furtherembodiments, the change in shape of the piezoelectric structure 106 maytake the form of the piezoelectric structure 106 deflecting toward (oraway from) the first electrode 104.

As the shape of the piezoelectric structure 106 changes, a value of theelectrical property of the piezoelectric biosensor 100 varies. Forexample, when the shape of the piezoelectric structure 106 is the firstshape, the biosensor may have a first potential between the firstelectrode 104 and the second electrode 108; when the shape of thepiezoelectric structure 106 is the second shape, the biosensor may havea second potential between the first electrode 104 and the secondelectrode 108 different than the first potential; and when the shape ofthe piezoelectric structure 106 is the third shape, the biosensor mayhave a third potential between the first electrode 104 and the secondelectrode 108 different than the first and second potentials.

Accordingly, the piezoelectric biosensor 100 may analyze the specificproperty of the bio-entities 120 in the sensing reservoir 116 based onchanges in the shape of the piezoelectric structure 106. For example,processing circuitry (not shown) may measure/detect the change inelectrical potential of the piezoelectric biosensor 100 at predefinedtime intervals as the fluid 118 is in the sensing reservoir 116. In someembodiments, the processing circuitry may measure/detect the change inelectrical potential of the piezoelectric biosensor 100 as a capacitanceby providing a bias voltage to the first I/O structure 112 andmeasuring/detecting changes in the capacitance of the piezoelectricbiosensor 100 via the second I/O structure 114 at the predefined timeintervals. In further embodiments, the bias voltage may be between about2 volts (V) and about 10 V. Based on the measured/detected capacitanceat the predefined time intervals, the processing circuitry may determinethe specific property of the bio-entities 120 in the sensing reservoir116.

Because the piezoelectric biosensor 100 is disposed on the semiconductorsubstrate 102, a form factor of the piezoelectric biosensor 100 may besmaller than other types of biosensors (e.g., spectrophotometers, platereaders, etc.). Thus, the piezoelectric biosensor 100 may reduce thecost to analyze a sample by providing an inexpensive Point-of-Care (PoC)biosensor application. Further, testing a sample (e.g., the fluid 118comprising the number of bio-entities 120) with the piezoelectricbiosensor 100 may be less time intensive than the other types ofbiosensors due to the piezoelectric biosensor 100 having a simplifiedbio-testing procedure (e.g., testing one sample to determine thespecific property of the bio-entities 120). Thus, the piezoelectricbiosensor 100 may further reduce the cost to analyze a sample.

FIG. 2 illustrates some other embodiments of the piezoelectric biosensor100 of FIG. 1 .

As shown in FIG. 2 , a first dielectric layer 202 is disposed on theback-side 102 b of the semiconductor substrate 102. In some embodiments,the first dielectric layer 202 may comprise, for example, an oxide(e.g., SiO₂), a nitride (e.g., SiN), an oxy-nitride (e.g.,SiO_(X)N_(Y)), or the like. In further embodiments, a second dielectriclayer 204 is disposed on the front-side 102 f of the semiconductorsubstrate 102. In further embodiments, the second dielectric layer 204may comprise, for example, an oxide (e.g., SiO₂), a nitride (e.g., SiN),an oxy-nitride (e.g., SiO_(X)N_(Y)), or the like. In yet furtherembodiments, the first dielectric layer 202 and the second dielectriclayer 204 may comprise a same material.

A structural support layer 206 may be disposed over the front-side 102 fof the semiconductor substrate 102. In some embodiments, the structuralsupport layer 206 is disposed on the second dielectric layer 204. Infurther embodiments, the structural support layer 206 providesstructural support for overlying elements of the piezoelectric biosensor100 (e.g., the first electrode 104, the piezoelectric structure 106, thesecond electrode 108, etc.). In yet further embodiments, the structuralsupport layer 206 may comprise, for example, polysilicon.

In some embodiments, an opening 208 is disposed directly beneath thepiezoelectric structure 106. The opening 208 is configured to reduce astiffness of a portion of the piezoelectric biosensor 100 directlybeneath the piezoelectric structure 106, such that the piezoelectricstructure 106 may change its shape based on the number of bio-entities120 in the sensing reservoir 116. In further embodiments, sides of theopening 208 extend into the semiconductor substrate 102 from theback-side 102 b of the semiconductor substrate 102.

In some embodiments, the opening 208 is defined by a bottom surface ofthe structural support layer 206, opposite sidewalls of the seconddielectric layer 204, opposite sidewalls of the semiconductor substrate102, and opposite sidewalls of the first dielectric layer 202. Forexample, a top of the opening 208 may be defined by a bottom surface ofthe structural support layer 206, and sides of the opening 208 may bedefined by the opposite sidewalls of the first dielectric layer 202, theopposite sidewalls of the semiconductor substrate 102, and the oppositesidewalls of the second dielectric layer 204, respectively. In furtherembodiments, the opposite sidewalls of the first dielectric layer 202,the opposite sidewalls of the semiconductor substrate 102, and theopposite sidewalls of the second dielectric layer 204 are substantiallyaligned, respectively.

In some embodiments, the sides of the opening 208 are sloped. Forexample, opposite sides of the opening 208 may slope toward one anotherfrom a bottom surface of the first dielectric layer 202 to the bottomsurface of the structural support layer 206. In further embodiments, theopposite sidewalls of the first dielectric layer 202 may be spacedfurther apart than the opposite sidewalls of the semiconductor substrate102. In yet further embodiments, the opposite sidewalls of thesemiconductor substrate 102 may be spaced further apart than theopposite sidewalls of the second dielectric layer 204.

A third dielectric layer 210 may be disposed between the structuralsupport layer 206 and the first electrode 104. In some embodiments, thethird dielectric layer 210 contacts both the first electrode 104 and thestructural support layer 206. In further embodiments, the thirddielectric layer 210 may comprise, for example, an oxide (e.g., SiO₂), anitride (e.g., SiN), an oxy-nitride (e.g., SiO_(X)N_(Y)), or the like.In yet further embodiments, the third dielectric layer 210 may comprisea same material as the first dielectric layer 202 and/or the seconddielectric layer 204.

In some embodiments, outermost sidewalls of the second electrode 108 aredisposed between outermost sidewalls of the piezoelectric structure 106.In further embodiments, the outermost sidewalls of the piezoelectricstructure 106 are disposed between outermost sidewalls of the firstelectrode 104. In further embodiments, the passivation layer 110 maycontact the second electrode 108, the piezoelectric structure 106, thefirst electrode 104, and the third dielectric layer 210.

In some embodiments, the first I/O structure 112 may be disposed on afirst side of the sensing reservoir 116, and the second I/O structure114 may be disposed on a second side of the sensing reservoir 116opposite the first side of the sensing reservoir 116. In otherembodiments, the first I/O structure 112 and the second I/O structure114 may be disposed on a same side of the sensing reservoir 116. Infurther embodiments, the second I/O structure 114 may have an uppersurface disposed over an upper surface of the first I/O structure 112.In other embodiments, the upper surface of the first I/O structure 112may be about co-planar with the upper surface of the second I/Ostructure 114.

FIG. 3 illustrates some other embodiments of the piezoelectric biosensor100 of FIG. 1 .

As shown in FIG. 3 , the opening 208 extends from the bottom surface ofthe first dielectric layer 202 into the structural support layer 206,such that a first bottom surface of the structural support layer 206defines a top of the opening 208. In such embodiments, oppositesidewalls of the structural support layer 206 may be substantiallyaligned with the opposite sidewalls of the first dielectric layer 202,the opposite sidewalls of the semiconductor substrate 102, and theopposite sidewalls of the second dielectric layer 204, respectively. Infurther embodiments, the structural support layer 206 may have a secondbottom surface that is disposed between the first bottom surface of thestructural support layer 206 and the front-side 102 f of thesemiconductor substrate 102. In yet further embodiments, the secondbottom surface may be disposed on opposite sides of the opening 208.

In some embodiments, the first electrode 104 comprises a first metalstructure 304 disposed on a first adhesion structure 302. In furtherembodiments, the first adhesion structure 302 is disposed on the thirddielectric layer 210. In further embodiments, the first adhesionstructure 302 is configured to improve adhesion of the first electrode104 to the third dielectric layer 210. In further embodiments, the firstadhesion structure 302 comprises a metal based oxide, for example,titanium dioxide (TiO₂), a ruthenium oxide (RuO_(X)), indium tin oxide(ITO), some other metal based oxide, or a combination of the foregoing.In yet further embodiments, the first metal structure 304 comprises, forexample, Ti, Pt, Cu, Au, Al, Zn, Sn, Ru, some other metal, or acombination of the foregoing.

In some embodiments, the second electrode 108 comprises a second metalstructure 308 disposed on a second adhesion structure 306. In furtherembodiments, the second adhesion structure 306 is disposed on thepiezoelectric structure 106. In further embodiments, the second adhesionstructure 306 is configured to improve adhesion of the second electrode108 to the piezoelectric structure 106. In further embodiments, thesecond adhesion structure 306 comprises a metal based oxide, forexample, TiO₂, RuO_(X), ITO, some other metal based oxide, or acombination of the foregoing. In further embodiments, the second metalstructure 308 comprises, for example, Ti, Pt, Cu, Au, Al, Zn, Sn, Ru,some other metal, or a combination of the foregoing.

In some embodiments, the passivation layer 110 comprise a fifthdielectric layer 312 disposed on a fourth dielectric layer 310. Infurther embodiments, the fourth dielectric layer 310 is disposed on thethird dielectric layer 210, the first electrode 104, the piezoelectricstructure 106, and the second electrode 108. In further embodiments, thefourth dielectric layer 310 may have a higher dielectric constant thanthe fifth dielectric layer 312. For example, the fourth dielectric layer310 may have a dielectric constant greater than 3.9 (e.g., a high-kdielectric), and the fifth dielectric layer 312 may have a dielectricconstant less than or equal to 3.9 (e.g., SiO₂ and/or a low-kdielectric). In further embodiments, the fourth dielectric layer 310 maycomprise a metal based oxide, for example, Al₂O₃. In yet furtherembodiments, the fifth dielectric layer 312 may comprise, for example,an oxide (e.g., SiO₂), a nitride (e.g., SiN), an oxy-nitride (e.g.,silicon oxy-nitride (SiO_(X)N_(Y)), or the like.

In some embodiments, the first I/O structure 112 comprises a secondconductive structure 316 disposed on a first conductive structure 314.In further embodiments, the first conductive structure 314 is disposedon the passivation layer 110 and the first electrode 104. In furtherembodiments, the first conductive structure 314 comprises, for example,Ti, Au, Pt, Al, some other conductive material, or a combination of theforegoing. In further embodiments, the second conductive structure 316comprises, for example, Au, Ti, Pt, Al, some other conductive material,or a combination of the foregoing. In yet further embodiments, the firstconductive structure 314 and the second conductive structure 316comprise different materials.

In some embodiments, the second I/O structure 114 comprises a fourthconductive structure 320 disposed on a third conductive structure 318.In further embodiments, the third conductive structure 318 is disposedon the passivation layer 110 and the second electrode 108. In furtherembodiments, the third conductive structure 318 comprises, for example,Ti, Au, Pt, Al, some other conductive material, or a combination of theforegoing. In further embodiments, the fourth conductive structure 320comprises, for example, Au, Ti, Pt, Al, some other conductive material,or a combination of the foregoing. In further embodiments, the thirdconductive structure 318 and the fourth conductive structure 320comprise different materials. In further embodiments, the firstconductive structure 314 and the third conductive structure 318 comprisea same material (e.g., Ti). In yet further embodiments, the secondconductive structure 316 and the fourth conductive structure 320comprise a same material (e.g., Pt).

FIGS. 4-14 illustrate a series of cross-sectional views of someembodiments of a method for forming the piezoelectric biosensor 100 ofFIG. 3 .

As shown in FIG. 4 , a first dielectric layer 202 is formed on aback-side 102 b of a semiconductor substrate 102. In some embodiments, aprocess forming the first dielectric layer 202 comprises depositing orgrowing the first dielectric layer 202 on the back-side 102 b of thesemiconductor substrate 102. In further embodiments, the firstdielectric layer 202 may be deposited or grown by, for example, thermaloxidation, chemical vapor deposition (CVD), physical vapor deposition(PVD), atomic layer deposition (ALD), sputtering, some other depositionor growth process, or a combination of the foregoing.

Also shown in FIG. 4 , a second dielectric layer 204 is formed on afront-side 102 f of the semiconductor substrate 102. In someembodiments, a process forming the second dielectric layer 204 comprisesdepositing or growing the second dielectric layer 204 on the front-side102 f of the semiconductor substrate 102. In further embodiments, thesecond dielectric layer 204 may be deposited or grown by, for example,thermal oxidation, CVD, PVD, ALD, sputtering, some other deposition orgrowth process, or a combination of the foregoing.

In some embodiments, the first dielectric layer 202 and the seconddielectric layer 204 may be formed at a same time by a single growthprocess. In further embodiments, before the first dielectric layer 202and/or the second dielectric layer 204 are formed, a planarizationprocess (e.g., mechanical grinding or chemical-mechanical planarization(CMP)) may be performed on the front-side 102 f and/or the back-side 102b of the semiconductor substrate 102 to reduce a thickness of thesemiconductor substrate 102 (e.g., a distance between the front-side 102f and the back-side 102 b). In yet further embodiments, the thickness ofthe semiconductor substrate 102 may be reduced to below about 750 μm(e.g., to about 725 μm).

As shown in FIG. 5 , a structural support layer 206 is formed over thesecond dielectric layer 204. In some embodiments, a process for formingthe structural support layer 206 comprises depositing the structuralsupport layer 206 on the second dielectric layer 204. In someembodiments, the structural support layer 206 may be deposited or grownby, for example, CVD, PVD, ALD, sputtering, molecular-beam epitaxy, someother deposition process, or a combination of the foregoing. In furtherembodiments, a planarization process (e.g., CMP) may be performed intothe first dielectric layer 202 to remove excess material that may bedeposited on the first dielectric layer 202 during formation of thestructural support layer 206.

Also shown in FIG. 5 , a third dielectric layer 210 is formed over thestructural support layer 206. In some embodiments, a process for formingthe third dielectric layer 210 comprises depositing or growing the thirddielectric layer 210 on the structural support layer 206. In furtherembodiments, the third dielectric layer 210 may be deposited or grownby, for example, CVD, PVD, ALD, thermal oxidation, sputtering, someother deposition or growth process, or a combination of the foregoing.More specifically, in some embodiments, the third dielectric layer 210may be deposited by plasma-enhanced chemical vapor deposition (PECVD).

As shown in FIG. 6 , a first adhesion layer 602 is formed over the thirddielectric layer 210. In some embodiments, a process for forming thefirst adhesion layer 602 comprises depositing the first adhesion layer602 on the third dielectric layer 210. In further embodiments, the firstadhesion layer 602 may be deposited by, for example, CVD, PVD, ALD,sputtering, electrochemical plating, electroless plating, some otherdeposition process, or a combination of the foregoing. In yet furtherembodiments, the first adhesion layer 602 comprises a metal based oxide,for example, TiO₂, RuO_(X), ITO, some other metal based oxide, or acombination of the foregoing. In yet further embodiments, the firstadhesion layer 602 is configured to improve adhesion between asubsequently formed layer and the third dielectric layer 210.

Also shown in FIG. 6 , a first metal layer 604 is formed over the firstadhesion layer 602. In some embodiments, a process for forming the firstmetal layer 604 comprises depositing the first metal layer 604 on thefirst adhesion layer 602. In further embodiments, the first metal layer604 may be deposited by, for example, CVD, PVD, ALD, sputtering,electrochemical plating, electroless plating, some other depositionprocess, or a combination of the foregoing. In yet further embodiments,the first metal layer 604 comprises, for example, Ti, Pt, Cu, Au, Al,Zn, Sn, Ru, some other metal, or a combination of the foregoing.

Also shown in FIG. 6 , a piezoelectric layer 606 is formed over thefirst metal layer 604. In some embodiments, a process for forming thepiezoelectric layer 606 comprises depositing or growing thepiezoelectric layer 606 on the first metal layer 604. In furtherembodiments, the piezoelectric layer 606 may be deposited or grown by,for example, sputtering, a spin-on process, CVD, PVD, ALD,molecular-beam epitaxy, some other deposition or growth process, or acombination of the foregoing. In yet further embodiments, thepiezoelectric layer 606 may comprise, for example, ZnO, GaN, PZT, someother piezoelectric material, or a combination of the foregoing.

Also shown in FIG. 6 , a second adhesion layer 608 is formed over thepiezoelectric layer 606. In some embodiments, a process for forming thesecond adhesion layer 608 comprises depositing the second adhesion layer608 on the piezoelectric layer 606. In further embodiments, the secondadhesion layer 608 may be deposited by, for example, CVD, PVD, ALD,sputtering, electrochemical plating, electroless plating, some otherdeposition process, or a combination of the foregoing. In yet furtherembodiments, the second adhesion layer 608 comprises a metal basedoxide, for example, TiO₂, RuO_(X), ITO, some other metal based oxide, ora combination of the foregoing. In further embodiments, the secondadhesion layer 608 is configured to improve adhesion between asubsequently formed layer and the piezoelectric layer 606.

Also shown in FIG. 6 , a second metal layer 610 is formed over thesecond adhesion layer 608. In some embodiments, a process for formingthe second metal layer 610 comprises depositing the second metal layer610 on the second adhesion layer 608. In further embodiments, the secondmetal layer 610 may be deposited by, for example, CVD, PVD, ALD,sputtering, electrochemical plating, electroless plating, some otherdeposition process, or a combination of the foregoing. In yet furtherembodiments, the second metal layer 610 comprises, for example, Ti, Pt,Cu, Au, Al, Zn, Sn, Ru, some other metal, or a combination of theforegoing.

As shown in FIG. 7 , a second electrode 108 is formed over thepiezoelectric layer 606. In some embodiments, a process for forming thesecond electrode 108 comprises forming a masking layer (not shown)(e.g., a positive/negative photoresist) on the second metal layer 610(see, e.g., FIG. 6 ). Thereafter, the second metal layer 610 and thesecond adhesion layer 608 (see, e.g., FIG. 6 ) are exposed to an etchant(e.g., a wet/dry etchant). The etchant removes unmasked portions of thesecond metal layer 610 and unmasked portions of the second adhesionlayer 608 to form a second metal structure 308 and a second adhesionstructure 306, respectively, thereby forming the second electrode 108.Subsequently, in some embodiments, the masking layer is stripped away.

As shown in FIG. 8 , a piezoelectric structure 106 is formed over thefirst metal layer 604. In some embodiments, a process for forming thepiezoelectric structure 106 comprises forming a masking layer (notshown) on the piezoelectric layer 606 (see, e.g., FIG. 6 ) and on thesecond electrode 108. Thereafter, the piezoelectric layer 606 is exposedto an etchant (e.g., a wet/dry etchant) that removes unmasked portionsof the piezoelectric layer 606, thereby forming the piezoelectricstructure 106. Subsequently, in some embodiments, the masking layer isstripped away.

As shown in FIG. 9 , a first electrode 104 is formed over the thirddielectric layer 210. In some embodiments, a process for forming thefirst electrode 104 comprises forming a masking layer (not shown) on thefirst metal layer 604 (see, e.g., FIG. 6 ), the piezoelectric structure106, and the second electrode 108. Thereafter, the first metal layer 604and the first adhesion layer 602 (see, e.g., FIG. 6 ) are exposed to anetchant (e.g., a wet/dry etchant). The etchant removes unmasked portionsof the first metal layer 604 and unmasked portions of the first adhesionlayer 602 to form a first metal structure 304 and a first adhesionstructure 302, respectively, thereby forming the first electrode 104.Subsequently, in some embodiments, the masking layer is stripped away.

As shown in FIG. 10 , a passivation layer 110 is formed over the thirddielectric layer 210, the first electrode 104, the piezoelectricstructure 106, and the second electrode 108. In some embodiments, aprocess for forming the passivation layer 110 comprises depositing afourth dielectric layer 310 covering the third dielectric layer 210, thefirst electrode 104, the piezoelectric structure 106, and the secondelectrode 108. A fifth dielectric layer 312 is then deposited coveringthe fourth dielectric layer 310.

Thereafter, a masking layer (not shown) is formed on the fifthdielectric layer 312. Subsequently, the fifth dielectric layer 312 andthe fourth dielectric layer 310 are exposed to an etchant (e.g., awet/dry etchant). The etchant removes unmasked portions of the fifthdielectric layer 312 and unmasked portions of the fourth dielectriclayer 310 to form a sensing reservoir 116 over the second electrode 108;a first I/O structure opening 1002 over the first electrode 104; and asecond I/O structure opening 1004 over the second electrode 108, therebyforming the passivation layer 110. Subsequently, in some embodiments,the masking layer is stripped away. It will be appreciated that, in someembodiments, multiple etchants may be used to form the passivation layer110. For example, a first etchant may remove unmasked portions of thefifth dielectric layer 312, and a second etchant different than thefirst etchant may remove unmasked portions of the fourth dielectriclayer 310.

In some embodiments, the sensing reservoir 116 is formed betweenoutermost sidewalls of the second electrode 108. In further embodiments,the first I/O structure opening 1002 is formed on a first side of thesensing reservoir 116. In further embodiments, the first I/O structureopening 1002 is formed extending through the passivation layer 110 froman upper surface of the fifth dielectric layer 312 to the firstelectrode 104. In further embodiments, the second I/O structure opening1004 is formed on a second side of the sensing reservoir 116 oppositethe first side. In further embodiments, the second I/O structure opening1004 is formed extending through the passivation layer 110 from an uppersurface of the fifth dielectric layer 312 to the second electrode 108.In yet further embodiments, the first I/O structure opening 1002 may bedisposed beyond outermost sidewalls of the piezoelectric structure 106,while the second I/O structure opening 1004 may be disposed between theoutermost sidewalls of the piezoelectric structure 106.

As shown in FIG. 11 , a first I/O structure 112 is formed over the firstelectrode 104 and electrically coupled to the first electrode 104. Inaddition, a second I/O structure 114 is formed over the second electrode108 and electrically coupled to the second electrode 108. In someembodiments, a process for forming the first I/O structure 112 and thesecond I/O structure 114 comprises depositing a first conductive layer(not shown) on the passivation layer 110, the first electrode 104, andthe second electrode 108. In some embodiments, the first conductivelayer lines the first I/O structure opening 1002, the second I/Ostructure opening 1004, and the sensing reservoir 116. In furtherembodiments, the first conductive layer may be deposited by, forexample, CVD, PVD, ALD, sputtering, electrochemical plating, electrolessplating, some other deposition process, or a combination of theforegoing. In yet further embodiments, the first conductive layer maycomprise, for example, Ti, Au, Pt, Al, some other conductive material,or a combination of the foregoing.

A second conductive layer (not shown) is then deposited on the firstconductive layer. In some embodiments, the second conductive layer fillsthe first I/O structure opening 1002, the second I/O structure opening1004, and the sensing reservoir 116. In further embodiments, the secondconductive layer may be deposited by, for example, CVD, PVD, ALD,sputtering, electrochemical plating, electroless plating, some otherdeposition process, or a combination of the foregoing. In furtherembodiments, the second conductive layer may comprise, for example, Ti,Au, Pt, Al, some other conductive material, or a combination of theforegoing. In yet further embodiments, the second conductive layer maycomprise a different material than the first conductive layer. It willbe appreciated that, in some embodiments, the first conductive layerand/or the second conductive layer may not be formed in the sensingreservoir 116. For example, a protective layer (not shown) (e.g.,positive/negative photoresist) may be deposited covering the sensingreservoir prior to depositing the first conductive layer and/or thesecond conductive layer.

Thereafter, a masking layer (not shown) is formed on the firstconductive layer. Subsequently, the first conductive layer is exposed toan etchant (e.g., a wet/dry etchant). The etchant removes unmaskedportions of the second conductive layer to form a second conductivestructure 316 and a fourth conductive structure 320, and removesunmasked portions of first conductive layer to form a first conductivestructure 314 and a third conductive structure 318, thereby forming thefirst I/O structure 112 and the second I/O structure 114. Subsequently,in some embodiments, the masking layer is stripped away. It will beappreciated that, in some embodiments, multiple etchants may be used toform the first I/O structure 112 and the second I/O structure 114. Forexample, a first etchant may remove unmasked portions of the firstconductive layer, and a second etchant different than the first etchantmay remove unmasked portions of the second conductive layer.

In some embodiments, the first I/O structure 112 is formed on the firstside of the sensing reservoir 116. In further embodiments, the first I/Ostructure 112 is formed extending through the passivation layer 110 fromthe upper surface of the fifth dielectric layer 312 to the firstelectrode 104. In further embodiments, the second I/O structure 114 isformed on the second side of the sensing reservoir 116 opposite thefirst side. In further embodiments, the second I/O structure 114 isformed extending through the passivation layer 110 from the uppersurface of the fifth dielectric layer 312 to the second electrode 108.In yet further embodiments, the first I/O structure 112 may be disposedbeyond the outermost sidewalls of the piezoelectric structure 106, whilethe second I/O structure 114 is disposed between the outermost sidewallsof the piezoelectric structure 106.

As shown in FIG. 12 , a protective layer 1202 is formed covering thepassivation layer 110, the first I/O structure 112, the second electrode108, and the second I/O structure 114. The protective layer 1202 isconfigured to protect the passivation layer 110, the first I/O structure112, the second electrode 108, and the second I/O structure 114 during asubsequent fabrication process(es). In some embodiments, a process forforming the protective layer 1202 comprises depositing the protectivelayer 1202 on the passivation layer 110, the first I/O structure 112,the second electrode 108, and the second I/O structure 114. In furtherembodiments, the protective layer 1202 may be deposited by, for example,a spin-on process, CVD, PVD, ALD, sputtering, some other deposition orgrowth process, or a combination of the foregoing. In yet furtherembodiments, the protective layer 1202 may comprise, for example, aphotoresist (e.g., a negative/positive photoresist), a dielectric (e.g.,SiO₂), a polymer, or the like.

As shown in FIG. 13 , an opening 208 is formed extending through thesemiconductor substrate 102 from the first dielectric layer 202 to thestructural support layer 206. In some embodiments, a process for formingthe opening 208 comprises flipping the semiconductor substrate 102(e.g., rotating 180 degrees), such that the back-side 102 b of thesemiconductor substrate 102 is facing an opposite direction than theback-side 102 b of the semiconductor substrate 102 faces duringformation of the protective layer 1202 (see, e.g., FIG. 12 ).

Thereafter, a masking layer (not shown) is formed on the firstdielectric layer 202. Subsequently, the first dielectric layer 202, thesemiconductor substrate 102, the second dielectric layer 204, and thestructural support layer 206 are exposed to an etchant (e.g., a wet/dryetchant). In some embodiments, the etchant is a dry etchant utilized ina reactive-ion etching (RIE) system. The etchant removes unmaskedportions of the first dielectric layer 202; unmasked portions of thesemiconductor substrate 102; unmasked portions of the second dielectriclayer 204; and unmasked portions of the structural support layer 206,thereby forming the opening 208. Subsequently, in some embodiments, themasking layer is stripped away.

In some embodiments, the opening 208 is formed with sloping sides. Infurther embodiments, the sloping sides of the opening 208 are formedsuch that opposite sloping sides of the opening 208 slope toward oneanother. In further embodiments, the sides of the opening 208 are formedsuch that the sides of the opening 208 extend into the structuralsupport layer 206 by a non-zero distance. In other embodiments, thesides of the opening 208 may be formed such that the sides of theopening 208 do not extend into the structural support layer 206.

As shown in FIG. 14 , the protective layer 1202 is removed. In someembodiments, a process for removing the protective layer 1202 comprisesflipping the semiconductor substrate 102 (e.g., rotating 180 degrees),such that the back-side 102 b of the semiconductor substrate 102 isfacing an opposite direction than the back-side 102 b of thesemiconductor substrate 102 faces during formation of the opening 208(see, e.g., FIG. 13 ). Thereafter, the protective layer 1202 may beremoved. In some embodiments, the protective layer 1202 may be removedby, for example, plasma ashing, exposure to a stripping agent (e.g., aphotoresist stripping solvent), or the like. In some embodiments, afterthe protective layer 1202 is removed, formation of the piezoelectricbiosensor 100 is complete. Because the piezoelectric biosensor 100 isformed on the semiconductor substrate 102, a cost to manufacture thepiezoelectric biosensor 100 may be less expensive than other types ofbiosensors (e.g., spectrophotometers, plate readers, etc.).

As illustrated in FIG. 15 , a flowchart 1500 of some embodiments of amethod for forming a piezoelectric biosensor is provided. While theflowchart 1500 of FIG. 15 is illustrated and described herein as aseries of acts or events, it will be appreciated that the illustratedordering of such acts or events is not to be interpreted in a limitingsense. For example, some acts may occur in different orders and/orconcurrently with other acts or events apart from those illustratedand/or described herein. Further, not all illustrated acts may berequired to implement one or more aspects or embodiments of thedescription herein, and one or more of the acts depicted herein may becarried out in one or more separate acts and/or phases.

At 1502, a first dielectric layer is formed on a first side of asemiconductor substrate, and a second dielectric layer is formed on asecond side of the semiconductor substrate opposite the first side. FIG.4 illustrates a cross-sectional view of some embodiments correspondingto act 1502.

At 1504, a structural support layer is formed over the second dielectriclayer, and a third dielectric layer is formed over the structuralsupport layer. FIG. 5 illustrates a cross-sectional view of someembodiments corresponding to act 1504.

At 1506, a first electrode is formed over the third dielectric layer, apiezoelectric structure is formed over the first electrode, and a secondelectrode is formed over the piezoelectric structure. FIGS. 6-9illustrate a series of cross-sectional views of some embodimentscorresponding to act 1506.

At 1508, a passivation layer is formed over the third dielectric layer,the first electrode, the piezoelectric structure, and the secondelectrode, wherein sidewalls of the passivation layer define sides of asensing reservoir that is disposed over the piezoelectric structure.FIG. 10 illustrates a cross-sectional view of some embodimentscorresponding to act 1508.

At 1510, a first input/output (I/O) structure is formed electricallycoupled to the first electrode, and a second I/O structure is formedelectrically coupled to the second electrode. FIG. 11 illustrates across-sectional view of some embodiments corresponding to act 1510.

At 1512, a protective layer is formed over the passivation layer, thefirst I/O structure, the first electrode, and the second I/O structure.FIG. 12 illustrates a cross-sectional view of some embodimentscorresponding to act 1512.

At 1514, an opening is formed directly beneath the piezoelectricstructure, wherein the opening extends into the semiconductor substratefrom the first side of the semiconductor substrate. FIG. 13 illustratesa cross-sectional view of some embodiments corresponding to act 1514.

At 1516, the protective layer is removed. FIG. 14 illustrates across-sectional view of some embodiments corresponding to act 1516.

In some embodiments, the present application provides a piezoelectricbiosensor. The piezoelectric biosensor comprises a semiconductorsubstrate. A first electrode is disposed over the semiconductorsubstrate. A piezoelectric structure is disposed on the first electrode.A second electrode is disposed on the piezoelectric structure. A sensingreservoir is disposed over the piezoelectric structure and exposed to anambient environment, where the sensing reservoir is configured tocollect a fluid comprising a number of bio-entities.

In other embodiments, the present application provides a piezoelectricbiosensor. The piezoelectric biosensor comprises a structural supportlayer that is disposed over a first side of a semiconductor substrate. Afirst electrode is disposed over the structural support layer. Apiezoelectric structure is disposed on the first electrode. A secondelectrode is disposed on the piezoelectric structure. A passivationlayer is disposed over the piezoelectric structure and has oppositesidewalls that define sides of a sensing reservoir, where the sensingreservoir is configured to receive a fluid comprising a number ofbio-entities. Sidewalls of the semiconductor substrate, which extendbetween the first side of the semiconductor substrate and an opposingsecond side of the semiconductor substrate, define an opening that isdisposed directly below the piezoelectric structure. Further, theopening is defined by a first bottom surface of the structural supportlayer.

In yet other embodiments, the present application provides a method forforming a piezoelectric biosensor. The method comprises forming a firstelectrode over a first side of a semiconductor substrate. Apiezoelectric structure is formed on the first electrode. A secondelectrode is formed on the piezoelectric structure. A passivation layeris formed on the second electrode, the piezoelectric structure, and thefirst electrode. A sensing reservoir is formed over the piezoelectricstructure, where forming the sensing reservoir comprises removing aportion of the passivation layer between outermost sidewalls of thesecond electrode. An opening is formed directly below the piezoelectricstructure, where the opening extends into the semiconductor substratefrom a second side of the semiconductor substrate opposite the firstside.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for forming a piezoelectric biosensor,the method comprising: forming a first electrode over a first side of asemiconductor substrate; forming a piezoelectric structure on the firstelectrode; forming a second electrode on the piezoelectric structure;forming a passivation layer on the second electrode, the piezoelectricstructure, and the first electrode; forming a sensing reservoir over thepiezoelectric structure, wherein forming the sensing reservoir comprisesremoving a portion of the passivation layer between outermost sidewallsof the second electrode; forming a first input/output (I/O) structureoverlying and electrically coupled to the first electrode, whereinforming the first I/O structure comprises forming a first opening in thepassivation layer and laterally spaced from the piezoelectric structure;forming a second I/O structure overlying and electrically coupled to thesecond electrode; and forming a second opening directly below thepiezoelectric structure, wherein the second opening extends into thesemiconductor substrate from a second side of the semiconductorsubstrate opposite the first side.
 2. The method of claim 1, whereinforming the first electrode comprises: depositing a first adhesion layerover the first side of the semiconductor substrate; depositing a firstmetal layer on the first adhesion layer, wherein a chemical compositionof the first metal layer is different than a chemical composition of thefirst adhesion layer; and etching the first metal layer; and etching thefirst adhesion layer.
 3. The method of claim 2, wherein forming thepiezoelectric structure comprises: depositing a piezoelectric layer onthe first metal layer; and etching the piezoelectric layer.
 4. Themethod of claim 3, wherein forming the second electrode comprises:depositing a second adhesion layer on the piezoelectric layer;depositing a second metal layer on the second adhesion layer, wherein achemical composition of the second metal layer is different than achemical composition of the second adhesion layer; and etching thesecond metal layer; and etching the second adhesion layer.
 5. The methodof claim 4, wherein: the first metal layer and the first adhesion layerare etched by a first etching process; the piezoelectric layer is etchedby a second etching process different than the first etching process;the second metal layer and the second adhesion layer are etched by athird etching process different than the second etching process; thesecond etching process is performed after the first etching process; andthe third etching process is performed after the second etching process.6. The method of claim 4, wherein: the chemical composition of the firstadhesion layer is the same as the chemical composition of the secondadhesion layer; and the chemical composition of the first metal layer isthe same as the chemical composition of the second metal layer.
 7. Amethod for forming a biosensor, the method comprising: depositing afirst electrode layer over a first side of a substrate; depositing apiezoelectric layer over the first electrode layer; depositing a secondelectrode layer over the piezoelectric layer; etching the secondelectrode layer to form a second electrode structure over thepiezoelectric layer; etching the piezoelectric layer to form apiezoelectric structure over the first electrode layer; etching thefirst electrode layer to form a first electrode structure verticallybetween the piezoelectric structure and the substrate; depositing apassivation layer over and covering the first electrode structure, thepiezoelectric structure, and the second electrode structure; etching thepassivation layer to remove a portion of the passivation layer thatoverlies the piezoelectric structure, thereby forming a sensingreservoir overlying the piezoelectric structure; and etching thesubstrate from a second side of the substrate opposite the first side ofthe substrate, thereby forming an opening in the substrate and laterallybetween opposite sidewalls of the piezoelectric structure.
 8. The methodof claim 7, further comprising: before the first electrode layer isdeposited, forming a structural support layer over the first side of thesubstrate, wherein the first electrode layer is deposited over both thefirst side of the substrate and the structural support layer.
 9. Themethod of claim 8, further comprising: before the structural supportlayer is formed, forming a first dielectric layer on the first side ofthe substrate, wherein the structural support layer is formed over thefirst dielectric layer.
 10. The method of claim 9, wherein forming theopening further comprises etching the substrate and the first dielectriclayer.
 11. The method of claim 10, wherein forming the opening furthercomprises etching the structural support layer.
 12. The method of claim11, wherein the structural support layer comprises a semiconductormaterial.
 13. The method of claim 7, wherein forming the passivationlayer comprises: depositing a first dielectric layer over and coveringthe first electrode structure, the piezoelectric structure, and thesecond electrode structure; and depositing a second dielectric layer onthe first dielectric layer.
 14. A method for forming a biosensor, themethod comprising: forming a structural support layer over a first sideof a semiconductor substrate; forming a first electrode layer over thestructural support layer and over the first side of the semiconductorsubstrate; forming a piezoelectric layer over the first electrode layer;forming a second electrode layer over the piezoelectric layer; etchingthe second electrode layer to form a second electrode structure over thepiezoelectric layer; after the second electrode structure has beenformed, etching the piezoelectric layer to form a piezoelectricstructure over the first electrode layer; after the piezoelectricstructure has been formed, etching the first electrode layer to form afirst electrode structure vertically between the piezoelectric structureand the structural support layer; forming a passivation layer overlyingthe first electrode structure, the piezoelectric structure, and thesecond electrode structure; forming a sensing reservoir overlying thepiezoelectric structure, wherein forming the sensing reservoir comprisesremoving a portion of the passivation layer that is disposed betweenopposite sidewalls of the piezoelectric structure; forming a firstconductive input/output (I/O) structure overlying and electricallycoupled to the first electrode structure; forming a second conductiveI/O structure overlying and electrically coupled to the second electrodestructure; and forming an opening in the semiconductor substrate andlaterally between the opposite sidewalls of the piezoelectric structure,wherein forming the opening comprises etching the semiconductorsubstrate from a second side of the semiconductor substrate opposite thefirst side of the semiconductor substrate.
 15. The method of claim 14,wherein forming the sensing reservoir over the piezoelectric structurefurther comprises removing a portion of the second electrode structurethat is disposed laterally between the opposite sidewalls of thepiezoelectric structure.
 16. The method of claim 14, wherein the sensingreservoir is formed with a lower surface that is defined by an uppersurface of the second electrode structure.
 17. The method of claim 14,wherein the opening is formed with angled sidewalls.
 18. The method ofclaim 17, wherein: the angled sidewalls of the opening comprise a firstangled sidewall and a second angled sidewall; the first angled sidewallis opposite the second angled sidewall; the first angled sidewall has afirst portion disposed laterally between the opposite sidewalls of thepiezoelectric structure; the second angled sidewall has a first portiondisposed laterally between the opposite sidewalls of the piezoelectricstructure; and both of the opposite sidewalls of the piezoelectricstructure are disposed laterally between a second portion of the firstangled sidewall and a second portion of the second angled sidewall. 19.The method of claim 14, wherein forming the sensing reservoir over thepiezoelectric structure further comprises forming a fluidic channelstructure over the passivation layer.
 20. The method of claim 19,wherein the fluidic channel structure is formed with opposite innersidewalls that are substantially aligned with opposite outer sidewallsof the second electrode structure.